Most of the proposed uses of guarana fall into line with these effects of caffeine. For example, in a double-blind, placebo-controlled study of 129 healthy young adults, one-time use of guarana plus vitamins and minerals improved mental function and reduced mental fatigue among those undergoing a battery of cognitive tests.
7
In another double-blind, placebo-controlled study, use of guarana alone or guarana plus
ginseng
appeared to
improve mental function
(though the study suffered from some design problems)
1
In two other studies, no benefits were seen.
2,3

Guarana has also been studied as a potential aid in fighting a common side effect of
chemotherapy
—fatigue.
8
In one randomized trial, 75 breast cancer patients undergoing chemotherapy were randomized to receive guarana (50 mg twice daily for 21 days) or placebo. Since this trail had a crossover design , both groups received the herb and the placebo but at alternate times. At the end of the trial, researchers found evidence that guarana was helpful in reducing fatigue.

Another double-blind, placebo-controlled study tested the effects of guarana plus
ephedra
for weight loss.
4
In this trial, a total of 67 overweight people were given either placebo or a combination of guarana and ephedra for a period of 8 weeks. The results showed significantly greater
weight loss
in the treated group than in the placebo group. However, ephedra is an unsafe substance. (See the
Ephedra
article for more information.)

Dosage

A typical dose of guarana supplies 50 mg of caffeine, about half the amount in a cup of strong coffee. However, a 1998 analysis of products on the market indicated that many guarana products contain less than the advertised amount of guarana.
5

Safety Issues

The side effects of guarana would be expected to be similar to those of tea or coffee, such as heartburn, gastritis, insomnia, anxiety, and heart arrhythmias (benign palpitations or more serious disturbances of heart rhythm).
6
Combination products containing guarana and ephedra would be expected to present additional risk. Finally, all drug interactions that can occur with caffeine would be expected to occur with guarana as well (see
Interactions You Should Know About
).

Young children, pregnant or nursing women, or people with heart disease should not use guarana.

Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a
medical condition.